Check your air filter.
My shee idled correctly and had no power. I had a hard time climbing a ridiculous hill in first gear, clutching, flat out.
Once on top. I stopped, cleaned the air filter, and it was done. It was ready to go again.
I don't rememeber who changed his plugs every 4 ride...are those 500 hours rides? You're crazy (or wealthy). Having a brand new plug won't change much compared to a used one. Just keep a new one with you and it will be perfect. Don't change it every four ride...it's no use and wasted money. I haven't changed any of my plugs yet (since july), and they have had a hard time (25:1 premix...got back to 50:1). Just keep a new one with you, and when you break it, change it, and that's as simple as this. Changing a plug is no big deal.